Percussion tools



March: 1955 R. GOLDSCHMIDT 2,704,059

PERCUSSION TOOLS Filed June 12, 1951 lrvv EN TOR RUDOLF eowscummr DECEASED av HELMUT J. coLocummT, ADMINISTRATOR {r dxkii United States Patent O PERCUSSION TOOLS Rudolf Goldschmidt, deceased, late of Sheffield, England, by Helmut J. Goldschmidt, administrator, Sheffield, England Application June 12, 1951, Serial No. 231,138

Claims priority, application Great Britain June 21, 1950 9 Claims. (Cl. 125-33) This invention relates to mechanically-operated percussion tools, such for example as power hammers, riveters, paving-breakers and rock drills of the type wherein the rotary motion of a driving motor is employed for producing reciprocating motion of a striker co-operatmg with a tool butt, tool holder or other anvil.

United States Patent No. 2,456,631, dated December 21, 1948, issued to Rudolf Goldschmidt relates to a percussion tool in which the striker is rotatable within a tubular body and capable of reciprocation longitudinally of the body. A motor is coupled with the striker for maintaining it in rotation, and the striker includes two diametrically-opposed centrifugal masses (hereinafter termed coupling means or fiyweights) constrained to follow the rotation and reciprocation of the striker and capable of bearing under the influence of centrifugal force on the interior surface of the body. This surface is shaped to provide helical tracks such that the reaction imposed by the helical tracks on the flyweights serves to convert the rotary motion of the striker into translatory motion. The land of the helical tracks is such that at the end of the in-(working) stroke of the striker the flyweights and the tracks co-operate to wind the striker outwards (i. e. away from the anvil member), the hand of the helical paths traced out by the flyweights during the working stroke being opposite to that of the helical tracks. The flyweights are rollers slidable in recesses in the striker, and the interior surface of the body is so shaped as to constrain the rollers when the striker is in the neighbourhood of its outer dead point (i. e. that remote from the anvil), to assume a reduced radius of rotation so rapidly that the rollers are thrown so deeply into the recesses that the effective components of the centrifugal forces act to retain the rollers pocketed in the recesses. The recesses are so inclined that the arresting of this translatory motion of the striker by the anvil causes the striker to apply to the rollers forces having components in the direction initiating the return movement of the rollers towards reengagement with the interior surface of the body.

If the cross sections of the helical tracks and of the flyweights are such that the flyweights can lock in the tracks under the influence of centrifugal force, e. g. if the tracks are parallel-sided grooves adapted to be engaged by parallel-sided rims of the flyweights (as in the arrangement described in the above-mentioned patent, there is the disadvantage that it is difficult to avoid unduly rapid acceleration of the striker when the flyweights engage in the grooves at the end of the working stroke, resulting in heavy stresses in and rapid Wear of the co-operating parts.

Accordingly one object of this invention is to provide an improved percussion tool of the type referred to wherein the above-mentioned disadvantage is reduced or avoided.

According to the invention there is provided a percussion tool comprising a hollow body provided with an anvil, a helical track, a striker capable of rotation about the axis of said track and of reciprocation axially of said track towards and away from said anvil, a motor coupled with 'said striker for maintaining it in rotation, coupling means displaceably mounted on the striker and capable of being urged into engagement with said helical track, the land of said track being such that when the motor is rotating the striker and said coupling means are engaged with said track the striker moves away from said anvil,

means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means whereby said coupling member is disengaged from said track during the whole of the stroke of said striker towards said anvil, said track being formed by a groove the sides of which diverge from one another in the direction towards the mouth of said groove.

If the engaging portion of the coupling means can engage the groove by radial displacement, provided the engaging portion is urged yieldingly into the groove at the instant when it is in register with the bottom of the groove, it will co-operate with the side of the groove that faces away from the anvil (hereinafter termed the accelerating side), and, if the engaging force is of suitable magnitude, the coupling means will progressively couple the striker to the helical thread during for example two-thirds of a revolution of the striker, the engaging portion of the coupling means riding up the said side of the groove during the accelerating period, but not so far as to top the ridge separating turns of the groove and to drop into the next turn. However, if the engaging portion happens to be in register with the ridge at the instant when it is urged yieldingly towards the groove, it will ride first on the side of the groove that faces towards the anvil (hereinafter termed the retarding side) and then on the accelerating side of the groove; the two impulses, inward and outward, thereby imparted to the striker cancel each other out, and the striker may therefore fail to move outwards, the coupling means jumping idly from turn to turn of the groove.

in order to overcome this disadvantage, in the preferred arrangement according to this invention, the grooveengaging portion of the coupling means is so constrained that when it approaches the helical groove its movement is in a direction having a component axially away from the anvil. In consequence, under a given engaging force, as the groove-engaging portion jumps from turn to turn of the helical groove, the accelerating impulses applied to the striker as the engaging portion co-operates with the accelerating side of the groove are stronger than the retarding impulses applied as the engaging portion cooperates with the retarding side of the groove, and the striker is accordingly accelerated axially away from the anvil until its axial velocity, steadied by friction damping, is such that the engaging portion remains at the bottom of the groove.

A further object of the invention is to provide a percussion tool of the type referred to, the manufacture of which is simplified as compared with the tool disclosed in the above-mentioned specification.

According to the invention also there is provided a percussion tool comprising an anvil, a striker, a motor for rotating said striker, means for effecting movement of said striker towards said anvil and means for effecting movement of said striker away from said anvil, said last-mentloned means comprising an externally screw-threaded shaft and means for coupling said striker to the screw thread of said shaft.

In order that the invention may be well understood and readily carried into effect, it will now be described in more degail1 with reference to the accompanying drawing, in w 1c Figure 1 is a view in longitudinal section of a tool according to one form of the invention, the parts being shown in the positions they assume when the striker has ust engaged the anvil of the tool and the coupling means are about to approach the helical track.

Figure 2 is a view of part of the tool of Figure 1 on a larger scale showing the coupling means in engagement with the helical track.

Flgure 3 is a side view, on a larger scale than Figure 1, showing a modification of part of the tool shown in Figures 1 and 2, and

Figure 4 is a part sectional view showing another modification of the tool shown in Figures 1 and 2.

Referring to Figures 1 and 2, the tool comprises a body formed by a tubular casing 1, to the upper end (referred to the drawing) of which is bolted the stator 2 of a high speed electric motor. The upper end of easing 1 is formed with an internal annular recess 3 which provides a seatmg for a cam ring 4 which is bolted to the casing 1 and the purpose of which will be hereinafter described. An anvil 5 is mounted in the lower end of easing 1 so as to be axially slidable with respect to the casing. It may also be rotatable with respect to the casing 1 if it is desired to impart to it a rotary motion, for example for drilling. A short-stiff radial compression spring 6 is fitted around the anvil between the lower inside face of the casing 1 and a radial flange 7 on the upper end of the anvil 5. Upward movement of the anvil is limited by a ring 8 fixed to the anvil below the casing 1. An externally screwthreaded shaft 9 integral with the anvil 5 and coaxial therewith extends upwardly within the casing 1, the upper end of shaft 9 having a counterbore to form a bearing'for the lower end of the motor shaft 10, which projects downwardly from the stator 2 to about half-way down the casing 1, and which is externally splined as shown for engagement with an internally-splined hole in the top of the striker 11, said hole communicating with a cylindrical bore 12 within the striker which can thereby pass freely over the thread on shaft 9. The thread on shaft 9 may be of any suitable form such as to form a helical groove the sides of which diverge from one another towards the mouth of the groove. In the arrangement shown, the thread is of symmetrical V-section. The upper surface of the striker 11 is provided with two diametrically opposite projections 14 which at appropriate times co-operate with earns 15 on the cam ring 4 in order to reverse the longitudinal movement of the striker 11 at the end of its upward stroke, i. e. in the direction away from the anvil 5 and thereby to effect movement of the striker towards the anvils, as described in the abovementioned patent. The means for coupling the striker 11 to the screw thread of shaft 9 at the end of the downward stroke of the striker in order to move the striker away from the anvil 5 include a lever 16 movable in a vertical slot 17 in the wall of the striker 11 and pivoted on a horizontal pin 18 the ends of which are suitably secured to the vertical walls of slot 17. The centre of gravity of lever 16 is at a higher level than the pivot pin 18 of the lever and is radially outward from said pin with respect to the axis of shaft 11. One arm of lever 16 projects downwards and inwards from the pin 18, the tip of said arm being shaped for engagement in the thread of shaft 11. This tip may be hardened or may consist of a hardened steel ball fitting loosely in a pocket or socket in the end of said arm, so that the tin can be easily and cheaply replaced in case of wear. The other arm of lever 16 forms the flyweight proper and projects substantially vertically upwards.

Assuming that the striker 11 is in the position shown in Figure 1, when motor 2 is started the rotation of motor shaft causes the striker 11 splined thereto to rotate, and due to the action of centrifugal force the upper arm of lever 16 is urged outwardly thereby causing the lower arm to move inwardly so that the tip thereof engages in the screw-thread on shaft 9. The latter being stationary, the lever 16 travels up the screw thread causing the striker to rise.

The upward movement of the striker 11 continues until, by virtue of the engagement of the projections 14 with the cams 15, the translatory motion of the striker is suddenly reversed. and the striker is thrown down on to the anvil 5. Means comprising surfaces 19 and 20 of the lever 16 and slot 17 respectively (see Fig. 2) are provided for maintaining the coupling means constituted by lever 16 disengaged from the screw thread during the whole of the axial movement of the striker 11 towards the anvil 5. As the striker is decelerated at the end of its upward movement. the inertia of the lever 16 causes it to tend to continue its upward movement and due to the centre of gravity being radially outside the bearing pin 18, the lever 16 moves in a clockwise direction as seen in Figure 1 so as to cause the fiat surface 19 thereon to engage with a wedging action with the inclined surface 20 of the upper wall of the slot 17 (see Figure 2), the lever 16 thereby being locked in a position in which the tip of the lever is disengaged from the screw thread.

During the whole of the subsequent downward movement of the striker, therefore, the lever 16 is locked in an inoperative position out of engagement with the screw thread and is prevented from bouncing over the turns of the screw thread. When the downward translatorv movement of the striker 11 is stopped by the anvil 5, the lever 16 is caused by its inertia to unwedge itself and to rock, with the assistance of centrifugal force, in anti-clockwise direction (Figure 1) into its operative position in which the tip of the lever is in engagement with the screw thread,

the lever being thereafter maintained in engagement with the screw thread, by the action of centrifugal force on the lever, until it is again rocked in clockwise direction as above described at the end of its upward stroke.

Due to the divergence of the sides of the screw thread the striker engages in the screw thread in a yielding manner thereby avoiding the above-mentioned disadvantage of a screw thread the sides of which are parallel.

The tip of the lever 16 is constrained, due to the pivotal mounting of the lever on pin 18, so as to move in an arcuate path such that as it approaches the screw thread the movement of the tip has a component directed away from the anvil, that is to say directed upwardly. With this arrangement, if as above-described the grooveengaging portion, that is to say the tip of the lever 16, rides first on one side and then the other of the thread, the accelerating impulses applied to the striker 11 as the tip of the lever 16 rides on the side of the thread facing away from the anvil are greater than the retarding impulses applied to the striker as the tip of lever 16 rides on the side of the thread facing the anvil 5. Referring to Figure 2 if a denotes the angle with the horizontal formed by a line passing through the axis of pin 18 and the point of contact between the tip of the lever 16 and the side of the thread, and [3 denotes the angle made with the horizontal by the sides of the screw thread, then the vertical thrust F1 acting upwardly on the striker 11 due to the reaction of the lever 16 on the pin 18 (neglecting friction) is P/ (tan ,6-cot a) where P is the force acting in the radially inward direction on the tip of the lever 16 due to centrifugal force acting on the lever. The force F2 acting downwardly on the striker when the tip of the lever 16 on the side of the screw thread facing the anvil 5 is P/ (tan [3+cot 0:). Thus F1 is always much larger than F2, and the striker is accordingly accelerated upwardly until its axial velocity, steadied by friction, is such that the tip of lever 16 remains at the bottom of the groove. It is necessary to avoid an arrangement in which the limiting case can arise where oz+l3=90 and F1 is therefore infinite as this would result in failure to cushion the shock of accelerating the striker upwards, the reaction then being directed along the line joining the axis of pin 18 to the point of contact between the tip of the lever 16 and the side of the screw thread. Damping of the oscillations of the lever is, naturally, caused by the friction between the tip of the lever and the sides of the screw thread, and may if desired be deliberately increased by frictionally restraining the pivotal movement of the lever 16, as for example by making the lever fit friction-tight on the pin 18 so as to produce for example a frictional force which is a considerable proportion, say one third, of the centrifugal force which acts on the lever. Alternatively a spring disposed in a transverse hole in lever 16 may be arranged to hear at each end on the side walls of the slot 17 so as to provide the desired fractional damping.

Since the lever 16 is always under strong centrifugal force while the tool is operating, it is desirable to provide on the striker 11 a stop, shown at 21 in Figure 2, which serves to prevent the tip of lever 16 from actually bottoming in the screw thread. There will be substantial friction between the lever 16 and the screw thread while the striker is being accelerated upwards, but when the striker is moving at uniform speed in conformity with the screw thread friction will to a large extent be relieved.

Upon each downward stroke of the striker 11 an impulse is imparted to the anvil 5 which as will be understood is adapted to receive a tool bit. The spring 6 serves to absorb part of the impact of the striker when the tool is removed from the work.

The rotor of the motor, and the brush gear if the motor is of the commutator type, may be slidable relatively to the casing 1, being biased to an intermediate position by light springs, so that they do not participate in the oscillations of the casing 1 produced by the reversals of the translatory movement of the striker 11.

If desired spring 6 may be omitted and the anvil 5 may be rigidly secured to the body 1, which may consist for example of a light steel shell. In another arrangement the anvil 5 may be slidable and rotatable in the body 1 and may be connected for example by three or more longitudinal rods to the cam ring 4, the latter being free to rotate so that under the reactive forces on the earns 15 when engaged by the projections 14 a rotary motion is imparted to the anvil. Such an arrangement is advantageous for example when the tool is employed to operate a rock drill. 1

In the arrangement shown in Figure 3, the lever 16 is pivotally mounted on a pin 13 the ends of which are carried by two arms 22, one of which is shown, on the ends of a band 23 encircling and secured to the outer surface of the striker 11. The lower end of lever 16 projects, as in the arrangement of Figures 1 and 2, through a slot in the wall of striker 11 so as to co-operate at appropriate times with the screw thread as above described, and the lever is also provided with a nose 24. The upper end of lever 16 is provided with a weight 25 such that the centre of gravity of lever 16 is above and radially outward, with respect to the axis of shaft 9, from the pin 18. An inertia ring 26, shown partly broken away, is fittted with a sliding fit around the striker 11 and a pin 27 on the striker projects through a vertical slot 28 in the inertia ring 26 so that the latter is capable of limited vertical movement with respect to the striker. In other respects the tool may be constructed as described with reference to Figures 1 and 2.

In the operation of the tool illustrated in Figure 3, as the striker attains its upper end position and the lever 16 is moved in clockwise direction by its inertia, the inertia ring 26 continues its upward movement and engages as shown inside the nose 24. The lever 16 is thereby locked in its inoperative position during the subsequent downward movement of the striker 11, until upon the striker being brought to rest by the anvil, the inertia ring 26 continues its downward movement and releases the lever 16 for engagement with the screw thread. If desired, instead of the inertia of lever 16 being employed to rock it in clockwise direction at the end of its upward travel, the upper part of the screw thread may be of gradually decreasing depth as indicated at 28a (Figure 1) for example over a part or the whole of the uppermost turn, so that towards the end of its upward translatory movement and before the cams 14 engage the earns 15 the lever is positively rocked into its inoperative position, in which the inertia ring 26 can engage within the nose 24 when the striker is momentarily brought to rest at the end of its upward movement.

In order to avoid excessive wear on the tip of the lever 16 it may be modified as shown in Figure 4, wherein instead of the tip of the lever 16 itself engaging the screw thread a separate screw thread engaging member is provided in the form of a nose 29 which is rotatably mounted in a recess 30 in the lever 16. Nose 29 is formed at one end with a pivot 31 which engages rotatably in the inner wall 32 of the recess 30, and is also formed with a groove 33 which serves as a race for ball-bearings 34 which bear against the side wall 35 of the recess 30. The outer end of the nose 29 is of frusto-conical form. It will be seen that with this arrangement the thread-engaging member, that is to say the nose 29, is free to rotate in one direction or the other according to whether it engages the upper or lower side of the groove in shaft 9, thereby reducing friction and wear as compared with an arrangement in which a fixed part of the lever 16 itself engages the groove. The screw thread may be of any suitable form other than the V-section shown in Figures 1 and 2, and in Figure 4 it is shown as having a wavy section. It may if desired be of sinusoidal or trapezoidal section.

Another expedient which may be adopted for reducing excessive friction and wear between the lever 16 and the screw thread is to arrange, by suitably dimensioning the lever 16, that the centrifugal force which urges the tip of the lever 16 into engagement with the thread is so small that the lever slips over the screw thread during a few rotations of the striker, instead of engaging with the screw thread immediately, until due to the difference in the impulses imparted to the lever as it bears first on the upper side and then on the under side of the screw thread it attains a sufficiently high vertical component of velocity to cause it to move up the screw thread in continuous engagement therewith.

If desired the lever 16 may be replaced by a slidable latch constrained to move relatively to the striker, preferably at such an angle to the axis of the shaft 9 that the upward force exerted on the striker when said latch engages the upper side of the screw thread is greater than the force exerted when the latch engages the lower side of the thread. Said latch may be arranged to move to engaging position under the action of a spring or a cen- 6 trifugally operated lever. The slopes of the two sides of the screw thread may if desired be different. i

What is claimed is:

1. A percussion tool comprising a helical track formed by a member having a groove the sides of which diverge from one another in the direction towards the mouth of said groove, a striker mounted for rotation about the axis of said track and for reciprocation axially of said track, an anvil disposed in a position to be struck by said striker towards the end of the axial movement of said striker in ,one direction, a motor coupled with said striker for retatably driving the striker coupling means displaceably mounted on said striker and engageable with said helical track, the land of said track being such that when said motor is rotating, said striker and said coupling means are engaged with said helical track and said striker moves away from said anvil, means for reversing the axial movement of said striker after a predetermined axial displacement thereof away from said anvil, and means for disengaging said coupling means from said helical track during the whole of the axial movement of said striker towards said anvil.

2. A percussion tool comprising a helical track, a striker mounted for rotation about the axis of said track and for reciprocation axially of said track, an anvil disposed in a position to be struck by said striker towards the end of the axial movement of said striker in one direction, a motor coupled with said striker for rotatably driving the striker coupling means displaceably mounted on said striker and engageable with said helical track, the direction of said track being such that with said coupling means engaging said track and said motor rotating, said striker moves away from said anvil, and means for reversing the axial movement of said striker after a predetermined axial displacement thereof away from said anvil, said helical track being formed by a member having a groove the sides of which diverge from one another towards the mouth of said groove and are directed in relation to the direction in which said coupling means approach said groove to engage therewith that the force exerted on said striker when said coupling means engage the side of said groove facing away from said anvil are greater than the force exerted on said striker when said coupling means engage the side of said groove facing towards said anvil.

3. A percussion tool as set forth in claim 2, wherein said coupling means are constrained to move in a path such that the groove-engaging portion of said coupling means approaches said groove in a direction having a component directed away from said anvil.

4. A percussion tool comprising a shaft formed with an external screw-thread the sides of which diverge from one another towards the mouth of said screw-thread, a striker mounted for rotation about said shaft and for reciprocation axially of said shaft, a motor coupled with said striker for rotatably driving the striker, an anvil disposed in a position to be struck by said striker towards the end of the axial movement of said striker in one direction, coupling means displaceably mounted on said striker and engageable with said screw-thread, the direction of said screw-thread being such that with said coupling means engaging said screw-thread and said motor rotating said striker, the latter moves away from said anvil, means for reversing the axial movement of said striker at the end of a predetermined axial movement thereof away from said anvil, and means for maintaining said coupling means disengaged from said screw-thread during the whole of the axial movement of said striker towards said anvil.

5. A percussion tool as set forth in claim 4, wherein said coupling means comprise at least one lever pivotally mounted on said striker and engageable under the action of centrifugal force due to rotation of said striker with said screw-thread.

6. A percussion tool as set forth in claim 4, wherein said coupling means comprise at least one lever pivotally mounted on said striker and engageable under the action of centrifugal force due to rotation of said striker with said screw-thread, and wherein said lever is formed with a surface operative to wedge with a surface of said striker for maintaining said lever out of engagement with said groove, said lever being movable by inertia, to a position in which said surfaces are wedged together, upon reversal of the axial movement of said striker at the end of its strike away from said anvil, and to move by inertia to free said surfaces from one another, upon said striker striking said anvil.

7. A perscussion tool as set forth in claim 4, wherein said coupling means comprise at least one lever pivotally mounted on said striker and engageable under the action of centrifugal force due to rotation of said striker with said screw thread, and wherein an inertia member is mounted on said striker for limited axial movement relative to said striker, said member in one axial position, which it assumes upon reversal of the movement of said striker away from said anvil engaging said lever and hold it out of engagement with said screw-thread, and in another axial position, which is assumes upon said striker striking said anvil, disengaging said lever thereby permitting said lever to engage with said screw-thread.

8. A percussion tool as set forth in claim 4, wherein said coupling means comprise at least one lever pivotally mounted on said striker and engageable under the action of centrifugal force due to rotation of said striker with said screw-thread and wherein an inertia member is mounted on said striker for limited axial movement relative to said striker, said member, in one axial position which it assumes upon reversal of the movement of said striker away from said anvil, engaging said lever and hold it out of engagement with said screw-thread, and in another axial position, which it assumes upon said striker striking said anvil, disengaging said lever thereby permitting said lever to engage with said screw-thread, and wherein for effecting disengagement of said lever from said screw-thread at the end of the movement of said striker away from said anvil, said screw-thread is formed with a portion of decreasing depth.

9. A percussion tool as set forth in claim 4, wherein said coupling means comprise at least one lever pivotally mounted on said striker and engageable under the action of centrifugal force due to rotation of said striker with said screw-thread, and wherein said lever is provided with a nose serving as the screw-thread engaging portion of said lever and rotatably mounted on said lever in such manner as to be capable of rotation under the action of frictional force between the sides of said screw-thread and said nose.

References Cited in the file of this patent UNITED STATES PATENTS 1,713,064 Weibull May 14, 1929 1,816,104 Weibull July 28, 1931 1,948,409 Weibull Feb. 20, 1934 2,407,604 Goldschmidt Sept. 10, 1946 2,456,631 Goldschmidt Dec. 21, 1948 

